how to block all website except google, yahoo, gmail, facebook..

RouterOS General
1

how to block all website (http and https) except google, yahoo, gmail and facebook.

2

You can use hotspot and add in “walled garden ip list” the sites you want to have access without authentication to hotspot

http://wiki.mikrotik.com/wiki/Manual:IP/Hotspot
http://wiki.mikrotik.com/wiki/Manual:IP/Hotspot/Walled_Garden